I find that weird to draw a line at 70 and not 99, why do you say that?
Maybe because of this from DDMS
"Q: How many secondary cards can I have?
A: Officially up to 99, but trying to add 99 cards to your account is a red flag and can trigger a financial review where you must submit your tax returns or else your accounts will be shut down. Some people have been shut down adding fake names as secondary users on their account."